Manganous hydroxide [manganese dihydroxide -- Mn(OH).sub.2 ] is conventionally obtained as a precipitate from manganous salt-containing liquors. These liquors are often produced as by-products from industrial processes, and usually contain various impurities. For example, in the preparation of hydroquinone, aniline is oxidized to benzoquinone using manganese oxides. After separation of the benzoquinone, the resulting liquor may contain manganous sulfate, sulfuric acid, ammonium sulfate, and alkaline earth metal sulfates along with additional impurities from the original manganese ore and from the processing plant. After purification this liquor is treated with aqueous ammonia to precipitate manganous hydroxide, which is normally highly contaminated with sulfates.
It has also been proposed to react solutions containing salts such as manganous halide or sulfate with an alkali metal or alkaline earth metal hydroxide. Under the proper conditions manganous hydroxide is precipitated and may be recovered. However, this method also suffers from the disadvantage that an elaborate purification is necessary to free the product from contamination by the halide or sulfate co-products.